1. Field of the Invention
The present invention relates to a testing device and a testing method for improving performance and safety of a battery such as a lithium ion battery enclosed in a portable telephone and other portable equipment.
2. Related Background Art
A rechargeable secondary battery enclosed in portable telephones and other portable equipment, a lithium ion battery, for example, has a lithium cobalt oxide compound for an anode, graphite for a cathode and organic electrolytes containing lithium salt. This secondary battery is comprised of a separator, which is a thin film that electrically insulates an anode and a cathode, and the anode, cathode and separator are rolled. In the case of a square shaped lithium ion battery, the rolled battery is transformed into a square shape, and is inserted into a square aluminum case, where electrolytes are filled, and is sealed.
The lithium ion battery is compact, light weight and has high energy density, and therefore the battery is constructed by thin anode and cathode films, using a chemically highly active cobalt oxide compound and organic electrolytes. In order to further decrease the size and weight of the battery, the above battery materials are contained in a light aluminum case.
In a lithium ion battery having this type of structure, an internal short of the anode and cathode may be caused by damage to the electrodes inside due to external pressure, resulting in abnormal heating and smoking of the battery. To prevent this, safety tests to insure safety in a damaged state have been performed by intentionally destroying the lithium ion battery (see Japanese Patent Application Laid-Open No. 2005-327616). For example, in this kind of safety test, a fully charged lithium ion battery is completely crushed (complete crush) by pressing a metal bar (round bar) from the outside, and the behavior of the battery after the complete crush, such as abnormal heating (about 160° C. or higher) or smoking, is checked. And only batteries which do not generate an abnormal state, including abnormal heating and smoking, are determined as non-defective batteries (OK batteries), thereby safety of the batteries is evaluated.
However it is rare that a force to cause a complete crush of a battery is applied from the outside to a general lithium ion battery enclosed in a portable telephone or the like, where a force to partially damage a battery (partial crush) is more likely to be applied. Hence the complete crush test of batteries is an extreme test, and is not appropriate as a test to determine the behavior of a battery when the battery is damaged in a normal use range of a portable telephone.